1. Field of the Invention
The present invention relates to a system for cooling a developer roll inside an image forming device.
2. Description of the Related Art
An image forming device, such as a laser printer, forms a latent image on a surface of a photoconductive drum by selectively exposing an area of the surface to light. Generally, the photoconductive drum is made of photoconductive material that is discharged by light, typically emitted by a laser. As the photoconductive drum rotates, the image forming device directs a laser beam across the surface of the photoconductive drum to discharge certain points. The laser beam “draws” letters and images to be printed as a pattern of electrical charges—the latent image. The latent image is developed into a visible or a toned image by using toner.
The toner is stored in a toner cartridge housing, a small container built into a removable casing. The image forming device gathers the toner from a sump within the toner cartridge housing and supplies it to a developer roll. The developer roll is a charged rotating roller. The toner moves from the developer roll onto the latent image on the photoconductive drum to create the toned image on the photoconductive drum. The toner cartridge housing is generally sealed to prevent toner leakage. Usually, J-seals are positioned proximate both ends of the developer roll to seal the toner cartridge housing on one hand and the developer roll on the other.
However, there is friction between the developer roll and the J-seals when the developer roll rotates. The friction creates heat inside the toner cartridge. Printing at higher speeds such as at or above 50 ppm causes extreme overheating, which is localized at the ends of the developer roll around the J-seals interface. Due to overheating, the toner leaks out through the J-seals. Once toner leakage at the J-seals begins, toner loss usually continues at a rapid rate, permitting several grams of toner per minute to escape into the image forming device. Such large amounts of toner losses severely affect cartridge yield, and may result in yields of several thousand pages fewer than expected. In addition, major print defects occur as the escaped toner from the toner cartridge can spill directly onto a transfer belt near the location of a first transfer or onto print media.
One solution to prevent overheating of the developer roll is to apply a lubricant to the ends of the developer roll or to the J seals to decrease the coefficient of friction. However, the lubricant applied to the J-seals or to the ends of the developer roll may contaminate the toner and ruin any printed image. Additionally, the lubricant may seep into other areas of the toner cartridge or the image forming device, causing unwanted damage and interfere with the proper operation of the unit. Another solution to prevent overheating of the developer roll is to utilize directed airflow, such as from a fan, to blow air across the entire length of the developer roll. However, this had been found to be ineffective in lowering the temperature of the developer roll by any significant amount.
It would therefore be desirable to provide an effective cooling system that obviates the above-mentioned problems.